A diffraction optical element has a grating configuration with a great number of grooves formed at a surface of a substrate which is formed of an optical material such as glass, resin or the like.
The diffraction optical element is used for various optical systems. The diffraction optical element is known to be used as, for example, a lens designed to collect diffraction light of a specific order to one point, a spatial low pass filter, a polarization hologram or the like.
The diffraction optical element has a feature of making an optical system compact. In addition, as opposed to refraction, diffraction of light is expressed to a higher degree as the light has a longer wavelength. Therefore, the diffraction optical element can be combined with an optical element of a refraction system to improve the chromatic aberration or the curvature of field in an optical system.
For assembling an optical device such as a camera or the like, the optical axes of the optical components need to be positionally aligned to each other at high precision. Patent Document No. 1 discloses a spherical lens having a marker for providing such position alignment at the center of the lens. Using such a marker, the optical components can be positioned at high precision.